The invention relates to tellurium-containing nanocrystalline materials, and to methods for making such materials.
Semiconductor nanocrystallites having radii smaller than the bulk exciton Bohr radius constitute a class of materials intermediate between molecular and bulk forms of matter. Quantum confinement of both the electron and hole in all three dimensions leads to an increase in the effective band gap of the material with decreasing crystallite size. Consequently, both the optical absorption and emission of nanocrystallites shift to the blue (i.e., to higher energies) as the size of the crystallite gets smaller.
Bawendi and co-workers have described a method of preparing monodisperse semiconductor nanocrystallites by pyrolysis of organometallic reagents injected into a hot coordinating solvent (J. Am. Chem. Soc., 115:8706 (1993)). This permits temporally discrete nucleation and results in the controlled growth of macroscopic quantities of nanocrystallites. The particle size distribution can be refined by size selective precipitation. The narrow size distribution of nanocrystallites can allow the particles to have narrow spectral width emissions. These techniques can yield excellent results in the production of selenium-containing II-VI semiconductor nanocrystallites.
The invention provides methods of synthesizing telluride semiconductor nanocrystallites. The nanocrystallites can have high quantum efficiencies and can have narrow size distributions. The telluride semiconductors have relatively smaller band gaps than their selenide and sulfide analogs, and can expand the range of colors available using II-VI photoluminescent nanocrystallites further into the far red range of the spectrum. In particular, cadmium telluride nanocrystallites can emit in wavelengths sufficiently long to make them suitable for use in multicolor detection schemes for whole blood diagnostics, where emission wavelengths of at least 630 nm can be preferred.
In one aspect, the invention features a nanocrystallite including a core of MTe, where M is cadmium, zinc, magnesium, mercury, or mixtures thereof. The core can have an overcoating on a surface of the core. The overcoating can be a semiconductor having a composition different from the core.
In another aspect, the invention features a nanocrystallite including MTe that can photoluminesce with a quantum efficiency of at least 20%.
In another aspect, the invention features a method of manufacturing nanocrystallites by injection of an M-containing compound, M being cadmium, zinc, magnesium, mercury, or mixtures thereof, and a Te-containing compound of the form 
where at least one of Z, Zxe2x80x2, and Zxe2x80x3 is an amide. Preferably, two of Z, Zxe2x80x2, and Zxe2x80x3 are, independently, amides, and more preferably three of Z, Zxe2x80x2, and Zxe2x80x3 are, independently, amides. The mixture is heated to grow the nanocrystallites. The heating can be controlled in such a way that the growth is controlled. The M-containing compound and a Te-containing compound can be premixed, or M and Te can be incorporated into different positions of a single molecule. The M-containing compound and the Te-containing compound can be injected sequentially or simultaneously. Additional M-containing compound, additional Te-containing compound, or a mixture thereof, can be added to the mixture during heating. An overcoating can be grown on a surface of the nanocrystallite. The nanocrystallites can be separated by size selective precipitation. An amine can be added to the mixture during size selective precipitation. The Te-containing compound can include a tris(dialkylamino)phosphine telluride. The Te-containing compound can have a boiling point of at least 200xc2x0 C., preferably 250xc2x0 C., and more preferably 280xc2x0 C., at one atmosphere.
In another aspect, the invention features a Te-containing compound of the form 
where at least one of Z, Zxe2x80x2, and Zxe2x80x3 is an amide, and a method of preparing a Te-containing compound including contacting P(Z)(Zxe2x80x2)(Zxe2x80x3) with Te.
The nanocrystallite can have a quantum efficiency of emission of at least 30%, 40%, 50%, 60%, or 70%. The quantum efficiency can be as high as 75%, 80%, 90%, 95% or 99%. The quantum efficiency can be between 20 and 99%, preferably between 30 and 99%, more preferably between 40 and 95%, and most preferably between 70 and 95%. The nanocrystallite can be a member of a size-selected population having no more than a 15% RMS deviation from mean diameter, preferably 10% RMS deviation or less, and more preferably 5% RMS deviation or less. CdTe nanocrystallites can photoluminesce and can have emission wavelengths in the range of 580 to 770 nm, preferably 550 to 780 nm, and more preferably 435 to 800 nm. The nanocrystallite can photoluminesce with a full-width at half maximum (FWHM) of 70 nm or less, preferably 45 nm or less, more preferably 20 nm or less, and most preferably 15 nm or less for a single nanocrystallite.